Variable resistance phonograph pickup



Dec. 20, 1949 w. s. BACHMAN 2,491,794

VARIABLE RESISTANCE PHONOGRAPH PICKUP Filed Nov. 28, 1944 5 Sheets-Sheet 1 AMPUF/ER Inventori William SBachman,

His tcorney.

Dec. 20, 1949 w. s. BACHMAN 2,491,794

VARIABLE RESISTANCE PHONOGRAPH PICKUP Filed Nov. 28, 1944 5 Sheets-Sheet 2 C019 TED W/TH l I WSCOUS wscous LUBRICANT Inventor: William S. Bachfnan,

His Attorney.

Dec. 20, 1949 w. SQBACHMAN 2,491,794

VARIABLE RESISTANCE PHONOGRAPH PICKUP Filed Nov. 28, 1944 3 Sheets-Sheet 5 Inventor: William S. Bachrnan,

by Jul/Z0 His Attorney.

Patented Dec. 20, 1949 VARIABLE RESISTANCE PHONOGRAPH PICKUP William S. Bachman, Fairfielr'l, Conn., assignor to General Electric Company, a corporation of New York Application November 28, 1944, Serial No. 565,537

15 Claims. 1

My invention relates to vibration translating devices such as phonograph pickups and more particularly to such devices for translating mechanical vibrations into electrical variations.

'In the construction of phonograph pickups it is desirable that the moving parts be made as light and as free moving as practicable to minimize damage to the record grooves and to enable the stylus to follow the grooves accurately over the desired range of frequencies of the recorded sounds. It is desirable also to minimize all extraneous sounds or noises and for this purpose the pickup should be designed to have minimum response to mechanica1 resonance effects. Furthermore, if true reproduction of the sound record is to be accomplished, the pickup response curve should be as nearly linear as possible within the desired range of frequencies.

It is an object of my invention to provide a vibration translating device including an improved arrangement for minimizing the vibrating mass of the device.

It is another object of my invention to provide a phonograph pickup including an improved arrangement for insuring linear response within a desired range of frequencies.

It is another object of my invention to provide a phonograph pickup including an improved vibration translating element of light and simple construction.

It is a further object of my invention to provide a phonograph pickup including an improved arrangement for damping low frequency vibrations to prevent excessive vibration of the stylus at the resonant frequency of the mechanical parts of the pickup.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a. perspective view of a portion of a sound reproducer including a turntable and tone arm provided with a pickup embodying my invention;

Fig. 2 is an enlarged view of the pickup shown in Fig. 1, with a portion of the casing broken away to show the details of construction of the head;

Fig-311s a sectional side elevation of the bee shownin Fig. 2; 1

Fig. 4 is a diagram of the electric circuit connections employed with the pickup;

Fig. 5 is a perspective view of a pickup head embodying a modification of my invention;

Fig. 6 is a sectional front elevation view of the head shown in Fig. 5;

Fig. '7 is a perspective View of a pickup head embodying a further modification of my invention;

Fig. 8 is an enlarged detail view of a portion of Fi Fig. 9 is a perspective view of a pickup head embodying another modification of my invention;

Fig. 10 is a perspective view, partly in section, of a further embodiment of my invention;

Fig. 11 is an enlarged exploded view of the stylus and support shown in Fig. 10;

Fig. 12 is a sectional side elevation of a pickup head illustrating a still further modification of my invention; 7

Fig. '13 is an enlarged bottom plan view of the stylus support of the head in Fig. 12; and

Fig. 14 is an exploded perspective view of the stylus arm and associated parts shown in Fig. 13.

Briefly, each of the pickups illustrated in the drawings is provided with a fine electrical resistance Wire and an arrangement for straining the wire in proportion to the vibrations of the stylus as it moves over a record sound track. The resistance wires are arranged so that they are never strained to their elastic limitsv and the variation in electrical resistance is directly proportional to the vibrations of the stylus- The stylus arm is a small lightweight resilient cantilever beam and the resistance wire in some of the pickups is secured transversely of the beam and in others it is secured directly to the beam longitudinally thereof; Distortion of the reproduced sounds because of tone arm resonance and other disturbances is minimized by damping arrangements particularly suited to the lightweight cantilever beam construction of the stylus porting cabinet; A pickup for translating into' electrical vibrations the sound vibrations" recorded on a disk record 5 is provided within a casing 5 at the end of the tone arm 3 and electrical connections are made to the amplifying apparatus (not shown) through wires '5. The pickup arranged in the casing 6, which is shown in detail in Figs. 2 and 3, comprises a supporting head 8 which is a block of suitable insulating material. A stylus arm 9 is rigidly secured to the head of a bolt I9 which in turn is securely clamped to the block 8 by a nut Ii tightened against a conducting plate I2. A suitable stylus or stylus point 53, which may be a sapphire or other jewel, is mounted or otherwise provided at the outer end of the arm 9 so that when the stylus moves over the sound track of a record it is displaced laterally and bends the arm 9 as a cantilever beam. In order to translate the vibrations of the arm 9 into electrical vibrations, a fine resistance wire I4 is secured to the arm 9 and is held under tension by a pair of conducting springs I5. The arrangement is such that the wire is strained by the vibrations of the arm 9 and its resistance varies in proportion to the strain. The wire is wound one and one-quarter times about two insulating posts It which act as snubbers. The wire is secured at its midpoint to the arm 9, as indicated at I6 and the two straight portions on either side between the posts I6 and the arm are the portions of the wire which are strained by the vibration of the arm, the snubbers I6 preventing straining of the upright portions of the wire by the high velocity vibrations of the stylus produced by the record sound track.

The tension maintained by the springs I5 is such that the wire I4 is strained to about onehalf its elastic limit so that variations in strain both above and below the initial strain take place, it being obvious that when the arm 9 moves to one side the tension on one portion of the wire increases while that on the other portion decreases. In order to utilize the opposite changes in electrical resistance of the wire I4 on the two sides of the arm 9, the conducting springs I5 are connected to two of the wires I through suitable clips secured to the head 9 by screws I? which also hold the springs I5 in position, and the third conductor I is connected to the conducting strip I2 by a third screw I1 and is thereby electrically connected directly to the arm 9 through the bolt III. The wire I4 is connected in a balanced electrical circuit as shown in Fig. 4, the outer two conductors 1 connecting the springs I5 to the terminals of the primary winding I8 of a transformer I9. The midpoint of the wire I4 is connected through the arm 9 and the middle conductor I to one terminal of a battery 2!} the other terminal of which is connected to a midpoint tap on the primary Winding I8. When the arm 9 is in repose, the tension on the two sides of the wire I4 is equal and. the electrical circuit is balanced so that the same amount of current flows in the two halves of the primary winding I8. However, as soon as the arm 9 is displaced by vibrations of the stylus I3, the resistances of the two sides of the wire I4 vary oppositely and the current flow through the winding I3 increases in one direction or the other depending upon the direction of unbalance of the resistances of the two portions of the wire I4. Any variations in current in the primary winding I8 produce correspondin voltage changes in a secondary winding 2| of the transformer. The voltage changes in the secondary 2I are impressed on a control electrode 22 of an electron discharge device 23 4 which supplies the amplified voltages to a power amplifier 24 to drive a loudspeaker 25. The circuit arrangement of Fig. 4 is conventional and has been employed heretofore to amplify oppositely varying electrical quantities.

lhe wire I4 may be made of Nichrome or other suitable material and should be selected to have uniform elasticity and electrical resistance throughout its length. The diameter of the wire may be of the order of one one-thousandth of an inch. The dynamic mass of the cantilever beam or arm 9 may be made very small. The small dynamic mass enables the stylus I3 to follow the sound track readily with minimum possibility of damage and the tone arm may be counterbalanced so that a very small unbalanced weight, say one-half ounce or less, may be provided to hold the stylus in the record groove.

The construction of the pickup head illustrated in Figs. 5 and 6 is similar to that of Figs. 2 and 3 and corresponding parts have been designated by the same numerals. The construction differs from that of the first modification in-that the insulating head indicated at 26 is provided with a recess 21 at its forward end and horizontally mounted damping rods 28 are employed instead of the snubbers I6. The rods 28 are slidably mounted in openings in the head 26 on either side of the recess 2'! and the resistance wire I 4 is secured directly to the inner ends of the rods. The rods are maintained under tension by springs 29 which urge them outwardly away from the arm 9, and the electrical connections to the ends of the wire I4 are made through flexible wires 30 connected between the outer ends of the rods 28 and the outer two leads I. The tension of the springs 29 is adjusted to maintain the wire I4 under tension with a strain about half way to the elastic limit in the same manner as the wire I4 in Fig. 2. In order to provide a damping action and prevent distortion due to low velocity displacements of the arm 9, a viscous liquid is provided to lubricate the engagin surfaces of the rods 28 and the walls of the openings in the head 28. The fluid is selected so that at the velocities of the displacements produced by the vibration of the stylus I3 in a sound track the rods 28 will remain substantially stationary. However, when displacements at lower velocities occur, the rods will move and minimize strain in the wire I4. One suitable liquid for lubricating these bearings is a solution of polymerized isobutylene in mineral oil.

The precise values of friction and damping efiect necessary to provide the required frequency characteristics may be determined in accordance with the well-known principles of mechanics applicable to vibrating systems including elastic elements.

In the pickup of Figs. 7 and 8 an arrangement is provided for locating the portions of the resistance wire which are to be strained in positions longitudinally of the pickup head. As shown in Fig, '7, an insulating head 3| is provided with a downwardly opening recess 32. A stylus arm 33 similar to the arm 9 of Figs. 2 and 5 is mounted in the forward end of the head 3| on an upright conducting member or post 34. Rigidly secured to the base of the arm 33 are two small rods 35 which constitute bell cranks moving with the vibrations of the arm 33. The details of con struction of the arm 33 and the bell cranks 35 are clearly shown in Fig. 8. The bell cranks are tied to the arm by a resistance wire 31 and flex with the arm in accordance with its vibrations.-

A block. of insulatingtmaterial'is:mounted:in,

the .recess 32'. so that it may slide longitudinally of the "heady :and-the two -..endsoi resistance wire:

31 are zconnectedtozposts-38-. on the block. 36, the

wirev being looped. around the :ends :of the :bell

cranks 35 andzaround the:arm;.33. FA spring 39 is secured .-between 1 the back .end wall of. recess. 32 and the-block 36. tomainta'imthe desired ten-'1. 2

sionuon the resistance wire-131. Electrical con nections to ,the :resistance Wire: are made-through fiexiblewiresj; connected. to posts 4|, at the rear M of the block=;36 and. connected :to theapostsu38 by suitable; wires142; thezwiresrfl preferablyipass under 'aeprotectiveisheet 43::ofi insu1ating material cemented :to' the block 36. The wires' 40- and the 1 post: :34 constitute the I three terminals not the i pickup-:and.are connectewto the three *conductors. "he The two portions :of: the wire 37- between the stylus-arm and theposts 38, therefore, may" be connectediin the electrical circuit of Fig.*-4

in the same manneras the"two'*portions--of the' wire: M in the embodiments of Figs. 1 to 6. a The head 3| may be made small and compact and maybe adapted readily-to accommodation-in a slendertone'arm andcoversuch-as illustrated in" Fig. 1.-

In Fig. there 1 illustrated a pickup ,which makes it possible to'employ-anormally unstressed resistance Wire which, when" stressed by vibration of the 'stylus, =is strainedalternately in tension and in compression: pickup-head '44 of suitable insulating material is provided-'with-"acenhigh {velocities-that sufllcientliorc'e canrbe developedyto produce-the required 'strain ofi theifine resistance-wire 48; and low velocitydisturbancesldo not produce corresponding resistance changes; The resistancewire. employed-intherpickupi'ot Fig.9 maytbe of the .samemateriaLandvdiam-a (55817125 that employed with the epickupsl-of Figs. e. 2 to 8 inclusive, a. resistance. wire having a .di.- I ameter. of OHEc-OI'iB-w-thOllStIldth of an inch and-1; having uniform .elasticityt. throughout its length beingsuitable for this purpose.

istic-of the .wire"is:-.linear...over a.wide range of tral'co'nducting post -45 on which is-mounted"a'" stylus-arm 46 of the cantilever beamtype employed-in -the pickupsdescribed'above. -Two*conducting-posts- 4-1- are provided one on either side of the arm- 46', and'a resistance wire 484s secured at its ends :in good electrical contact with the'""' posts -The Wire 48 is alsosecured "to the arm- 46- in the same manner asthe Wire Mis securedto the arm 9 in'Fig.-2. The wire 48 and-thd'portion' sound frequencies.

In Figs.'. 10 andallv I have illustrated a pickup.

construction employing a.variableresistance, .vi.-. bration. sensitive wire andswhich makesit possible tmpnovide.,veryeffeotive damping to. prevent distortions. due.;-.to vibrations .other. than. those. produced ;.by thesound track. .This pickup; as illustrated in',Fig- 10, comprises ahead 50 of insulating.materialprovided with a recess at its.for-

wardiend .in which-a. supporting -blockw5l is mountedon trunnions .52, onlyone of-v which is illustrated. ,The'. block 5! supports .aresilientj cantilever beam type stylus .arm 53 havinga jewelorl otherlsuitablestylu's point 54 mounted or otherwiseprovidedtat.itsother'end. As shown of the arm 4M0 which it 'is secured are embedded in a body-of resilientinsulating material =49'-which has loeerrillustrated as cemented or otherwisesecured to the underside of the head 44'.- -Any suitable-flexible insulating material which may be made-to closely: embed the wire=48 and: restrict its lateral movement may be employed: *One'ma terialsuitable for this tpurposeeisthat'soid under the trade name-of -Pyralin'."'=-When the stylus arm 46: is vibrated by displacement of the stylus I 3 as it moves along the soundtrack Ora-record;

the resistancesof the portions of -the wire 48-em-- beddeddn the material- -49 on either side of thearmt lfi ar'e:varied in proportion to the intensity of the :vibrations.

The' material 4 9- restricts lateral -movement of the "embedded wireand-*al though the wire constitutes a-long slendercolum n whichwould *re'adilybend up'on' application of: a

compressive force, the insulating material restrictsthis bending under high v'elocity stresses, and,. asa result, the wireis strained-both in com-as pressionxand. in tension. -:Thus,"ifor any-one displacement ofthe stylus arm, the portionsof wire 1 on one sideofsthe arm: is strainedsin compres as.

sionawhile match the *otherzsidevis strainediin tension, and as .thei'arm 4B- vibrates, this xalternatet and oppositerstraining of the portions .ofxthe wire 1: produces; proportional nalternatexi. and: opposite 2 variation's oitthe :electrical resistance .of thewire.

The pickupof Fig.. 9:' may be connecteddn: the:

electrical circuit QfFigs. 4 in.the manner *alreadym:

describedin order to reproduce. the Lrecorded. sound-..:;Strain-:of the :resistance' wirexis (produced: onlyat the high ivelocities produced rasi the-istyluss.

followsg-assound. track salt is on1y.-at'- relatively-i.

in Fig. 11, the armu53. has; an upwardly p'r0ject-, 7 ing lug 55 formed at its rear end which is fitted...

into a circular recess 56 infan uprightmetal pivot member or post 51. 'jTheilug'55 fits snugly in the.

recess 55 'and.is secured, therein by a suitable.

cement, and thepivot member 51 is pivotally mounted in the'blockfi'l' so that the arm 53 is mounted 'for rotation? on either of two axes at right angles to one another: v".The'trunnions'52 of the block 51- a'ndthepivot member '51; areall lubricated'with'a' dampingliquid of the same type as thatemploye'd ini theipickup'of Fig.'-'5: The viscous liquid on the bearingsurfaces of the'post 51 restr-ainsrotation of'the post when the arm- 53 is vibrated atthe high velocitiesofth'e-sound vi brations on arecordtr'ack; and, consequently; the arm 53 bends laterally in proportion to the intensities of the "sounds: In order to-limit rotation about thetrunnions-52-whenthestylus 54 is bearingon a=-record-,'a'-spring 58 1s provided be- ThissDring tween the head 50 and-the block 5 I; is selected to have sufficient "force to counterbalance'the unbalanced Weight ofthe tone armand maintain the stylus=53 in its desired position. i

In order to reproduce electrically-the vibrations of the stylusarmgresistance Wires 59 are secured to thes'ides of the s'tylus'arm 53' and. the 'endsof the wires adjacent the stylus-54 are soldered or otherwise suitably: secured in good electricalcontact with'the arm' 53 as indicatedat 60. Each of the wires- 59 h'as'a "straight"portion extendi-ng alongthearm-53 and: securely bonded to the 7 arm by resilient insulating cement ---indicatedat These. straightaportions aresecured on opposite sides of: the=stylus arm 53. and thereforet onlyoneof the straight portions :is visible insthe ,WhenZKthemstyIus-LEA is vibrate-dt -the-mw drawings.

arm 53 bends and the straight portions of the wires 59, which are bonded to the arm, are strained in proportion to the bending of the arm. One portion of the wire is strained in tension and the other in compression durin the bending of the arm and the electrical resistances of the wires are varied accordingly. The resistance portions therefore can be connected in the electricai circuit of- Fig. 4 in the same manner as the variable resistance portions -of the resistance wires of the other pickups described. The stylus arm 53 has been illustrated as having greater depth than width so that there will be little bending of this arm'in the vertical plane. However, should the arm 53 bend in the vertical plane both straight portions of the wire 59 will be strained equally and any variations in resistance will be equal and opposite; therefore, changes in current flowing in the two portions will balance out in the primary of the transformer I 8. In some applications, however, it may be desirable to employ only one of the wires 59, the electrical circuit in this case being the same as that in Fig. 4 with one of the outer conductors I disconnected or removed. When only one resistance wire is employed in this manner, bending of the arm 53 in the vertical plane tends to produce a strain in the wire and a corresponding change in current through the wire which cannot be balanced out in the electrical circuit. For this reason, when a single straight portion of the wire 59 is employed, it is located as nearly as possible along the neutral axis of the arm 53 when considered as, a cantilever beam. The neutral axis is a line along which there is no strain in the material of the beam, the material on one side being strained in compression and on the other side in tension. By locating the resistance wire along the neutral axis, straining of the wire due to bending of the beam in the vertical plane is minimized.

The damping arrangement including the pivota1 support of the stylus arm on horizontal and upright axes makes it possible to minimize distortions due to vibrations such as mechanical vibrations of the pickup and associated parts at the resonant frequency of the assembly. Other low frequency vibrations such as those due to unevenness in the surface of the record disk are also damped out. Since the dynamic mass of the stylus is very small, the pickup arm may be mounted with a very small unbalanced weight and the stylus 54 may therefore be made to follow the record groove and trace the record vibrations with accuracy over a wide band of frequencies.

In the pickup illustrated in Figs. 12, 13 and 14, there is provided a compact arrangement for mounting a stylus arm of the type employed in the pickup of Fig. and including a similar damping arrangement of the pivotal supports for the stylus arm. As illustrated in Fig. 12, the pickup comprises a head 62 constructed of rigid insulating material and provided with a rectangular opening 63 extending from the top to the bottom thereof near the forward end of the head. A rocker block 64 for supporting a stylus arm 65 is pivotally mounted within the recess 63 on a shaft 66. light metal such as aluminum and the size of the block is such that its pivotal movement within The block 64 may be constructed ofv the recess 63 is limited by the walls of the recess.

A spring 6! is mounted-in recesses 68 and 69 in the head 62 and block 64, respectively, and biases the block 64 forwardly in a clockwise direction, as viewed in Fig. 12, so that the front end of the block 64 rests against the front wall of the recess 63. A drill hole 10 in the forward wall of the recess 63 is present merely because it is formed during the drilling of the recess 68 in the head at the rear wall of the recess. The arm 65 is mounted on an upright post TI on washers 12 of resilient insulating material such as Pyralin which hold the post in spaced relation to the sides of an upright bore '13 in the rocker block 64. A third washer 14 of Pyralin or other suitable insulating material is provided at the lower end of the post H in an enlarged portion of the upright bore 13. The two washers l2 and the washer 14 provide the desired damping action to suppress undesired vibrations of the stylus arm. The stylus arm 65 is a forwardly extending portion of a resilient bar 15 which extends rearwardly from the post H in a downwardly opening recess 16 in the head 62 and is soldered to the lower end of a conducting metal sleeve H. The rear end of the bar 15 is upturned at 78 and fits within a recess 19 in the head which serves to locate the bar during assembly of the pickup. The portion of the bar 15 between the sleeve H and the post ll is bent sinuously in a horizontal plane, as indicated at 80, to provide a spring which cooperates with the spring 61 to determine the position of the block 64 when the stylus is resting on a record. The stylus or point is indicated at 8| and may be a sapphire or other suitable jewel secured at the end of the arm 65.

The details of construction of the post II and the method of supporting the stylus arm 65 are shown in Figs. 13 and 14. The post is provided with an enlarged lower end 82 of square cross section and having a shoulder 83 of oblong cross section at the top thereof. A diagonal slot 84 in the head portion 82 receives the rod '15 which is secured therein by soldering. A metal shield 85 is secured on top of the head 82 and has an opening 86 of the same oblong shape as the shoulder 83, the shoulder being of the same height as the thickness of the shield 85. The oblong shape of the shoulder holds the shield in the desired position with respect to the stylus arm. The shield 85 is provided with downwardly extending side members 81 which prevent injury to the arm 65 during the handling of the pickup head. Two lengths of fine resistance wire 88 are secured on either side of the stylus arm 65 over a paper insulator 89 shaped, as shown in Fig. 14, to cover the sides of the square head 82 and of the stylus arm 65. The paper insulator 89 is cemented to the block 82 and stylus arm 65 by a suitable resilient insulating cement such as that sold under the trade name Giyptal. The two lengths of resistance wire 88 are secured to metal foil ribbons 90 and the wires, together with the ribbons, are cemented to the sides of the block 82 and arm 65 over the paper insulator 89 with Glyptal or other suitable resilient cement. These wires are similar in all respects to the wires described in connection with the other embodiments of the invention. The forward ends of the Wires 88 are soldered or otherwise suitably secured to the stylus arm 65, as indicated at 9|. The positions of the wires 88 along the stylus arm 65 are made alike on both sides and preferably the wires lie along the neutral axis of the arm with respect to bending in a vertical plane. This position of the wires minimizes or prevents distortion due to bending of the stylus arm 65 laterally in directions other than the normal direction of vibration of the stylus 8| when following the sound track of a record. The ribbons 9D areT'c'onnected' bywirs 92 to'ftwo upright sleeves saor the sam'e'construction'as the sleeve 71 and mounted in the head rearwardly of the recess 63. Only one ofthe sleeves 93 isshown in the drawings since the view of the head .62 in .,Fig. 12. is a section along. thecenterline thereof. The sleeves 93 are rivetedin position onthe head 62 in the same manner as thesleeve .Ti-an dithe .wires 92 areI'soldered t'ozthe lower ends of the respective sleeves. The three leads indicated at J in Fig. .4 may be connected tothelsleeve i1 and the two sleeves 93 so that-the pickup may be-connectedin thecircuit ofFigl 4in thesame manner as. th'e other pickupsdescribed. above; the operation orthe pickup ofFig. lZ beingZiessentiaHy the same asthat of-the pickup of. Fig. 10.

.Thepressures -exerted by the springs 61:: and

Damping to preventinterferencedue .to' me- :chanical resonance-frequencies of'the pickup and-tone arm is-provided by the resilientswashers I2 and the washer 14. These washers perform the function of theviscouslubricant in'the pickup ofaFig. and:preventtrotation of5theapost 1| upon lateral displacement of the stylus arm 65 atthehigh velocities produced by=.the; -recorded I .soundtrack. The -:.wa'shers,;. togetherwith z the 1 springs Bland 8'0;'alsoi-afiord movement of the stylusarm 65-without= bendingiwhen lowivelocityforces. are; applied in1-any direction.

It:is-readily=apparent from the rforegoin'githat l I- have :provided .a vibration;translating 'device -having' vibrating parts of ;very: zs-mall mass' and a very simple and effective telement for-translatingmechanical vibrations riintoarfoorresponding electrical variations: 'Furthermora simple -and efiectivesdampingarrangements are provided for preventing distortion due to mechanical vibrations at undesired fret1ue'ncies.'- It will readily be apparent to those. skilled intheart-that the pickups which I have illustrated-rand;described may be rearranged in many ways to utilize the features ormyinvention.

Although I have described: and illustrated my invention as applied to phonograph reco'rd'i'disks provided..with the so-called '-laterally out sound tracks, itis obvious that the invention is equally applicable to other types of-sound tracks.-. For .-.example,-it may be applied :totthe hilliarid 'dale type recording, it being necessary merely to dispose the elements of the pickup so that vibration laterally of the longitudinal axis of the stylus arm and in the direction determined by the type of sound track produces the required strain in the resistance wire.

Although I have illustrated and described particular embodiments of my invention in connection with a single type of sound track, other applications will readily occur to those skilled in the art. I do not, therefore, desire my invention to be limited to the particular arrangements illustrated and described and I intend by the appended claims to cover all modifications which fall within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A phonograph pickup comprising a support- 7 .10 i ihgliead, 'astylus arm having 'a-styluslpoint at one .endand beingsupported onMsaid-"heaG at its otherrend wherebysaid -arm is vibrated by vibration-sci. said-stylus point,- an electrical re- 5 'sistance wire havingone of its'ends secured on said headand its other end attached to said farm to be strained by vibrations of 'said-arm toyary the resistance of said wire accordance -with I I vibrations .ofsaid stylus point.

lo 2.. A. phonograph pickup comprising-asupportingchead a stylus -arm-having a stylus-point at oneend and beingsupported onsaid head at its other-endaanda resistance wire having one of its ends-secured to said head and its=otherend Hattachedto said arm to be strained by vibrations of-- said arm to .vary the' electrical-resistance of said wire in accordance with the vibrations of said .arm.

3. A phonograph. pickup comprising a =supporting head, a stylus armsupported at: oneend on said head and havinga stylus point at its Other-end adapted to be vibratedupommovemerit "along a record soundtrack-and an' elec- :trical resistance wire having its .endsconnected respectively 'to saidamr sand "saidi headand arranged to-bestrained mechanically by the vibra- 'tions ofsaid arm to'vary; theelectrical resistance :of said wireinaccordance-with the vibrations of said arm.

4; A phonograph pickup.comprising-a supporting head, 'a resilient stylus armsupported atone end on said head and --having -a stylus point at its othenendadapted to be vibratedupoii movement along a record sound tracktwhereby -isaid arm is stressed as a cantilever beam;- and; an

. electrical resistance.wire havingone of its'uends secured tosaid head and itsother end' attached to-said. arm to be strained upon bending of said riarm to vary theelectrical resistanceof-saidc-wire 4 in accordance-with the vibrations oi-said stylus 5 point.

-5. A phonograph pickup comprising-asupporting head, a stylus arm supported atonecend on -said-head and havinga stylus-point at its other endcadaptedto be vibrated upon movement along a recordsound track, and an-electr-ical resistance Wire-r--ha ving its .ends connected respectively to said-arm and to said headsaid wire beingstrained by the vibrations of said arm to Y varyw-thewelec- 5 trical resistance of saidwire accordance with the vibrations -of said arm.

.6. A phonograph pickup comprising rag-supportinghead; a stylus arm supported ati-oneriend on-saidhead and having a stylus: point at its other end adapted to be vibrated upon movement along .a .-record -sound-.-track;. an felectricar resistance wire having ca point mechanically: connected to said arnnand :means including-arresilient member mounted on said head and connected to another point of said wire for tensioning said wire between said head and said arm whereby said wire is strained in accordance with the vibrations of said arm and the electrical resistance of said wire is varied in proportion to 55 such vibrations.

7. A phonograph pickup comprising a supporting head, a stylus arm supported at one end on said head and having a stylus point at its other end adapted to be vibrated upon movement along a record sound track, and an electrical resistance wire having its ends mechanically connected to said head and its midportion mechanically connected to said arm to provide portions of said wire on either side of said arm, said portions be ing oppositely strained mechanically by vibrations of said arm whereby the electrical resistances of said portions of said wire are varied oppositely in proportion to the vibrations of said arm.

8. A phonograph pickup comprising a supporting head, a stylus arm supported at one end on said head and having a stylus point at its other end adapted to be vibrated upon movement along a record sound track, an electrical resistance wire mechanically connected to said arm, resilient means on said head for holding said wire under tension and for affording bodily movement of said wire with said arm, and means for damping high velocity movements of said resilient means whereby said wire is strained in accordance with vibrations of staid stylus point produced by a record sound track and the electrical resistance of said wire is varied in proportion to such vibrations.

9. A phonograph pickup comprising a supporting head, a stylus arm supported at one end on said head and having a stylus point at its other end adapted to be displaced laterally upon movement along a record sound track, a member movably mounted on said head, an electrical resistance wire connected to said arm and to said member, resilient means connected between said member and said head for holding said wire under tension and for affording movement of said wire bodily with said arm, and a coating of viscous fluid between said member and said head for damping high velocity movements of said member whereby said wire is strained in accordance with vibrations of said stylus point produced by a record sound track and the electrical resistance of said wire is varied in proportion to such vibrations.

10. A phonograph pickup comprising a supporting head, a stylus arm supported at one end on said head and having a stylus point at its other end adapted to be vibrated upon movement alond a record sound track, a pair of rods slidably mounted in said block one on either side of said arm, an electrical resistance wire having its midportion connected to said arm and its ends contions of said stylus point produced by a record sound track and the electrical resistance of said wire is varied in proportion to such vibrations.

1 A phonograph pickup comprising a supporting head, a stylus arm supported at one end on said head and having a stylus point at its other end adapted to be vibrated upon movement along a record sound track, a crank rigidly s cured to said arm adjacent said head to form bell crank with said arm, an electrical resistant wire connected to said crank, and means inclut ing a resilient member on said head for tensior ing said wire between said head and said crar and in a direction longitudinally with respect 1 said arm whereby said wire is strained upo vibration of said stylus point and the electric: resistance of said wire is varied in accordam with such vibrations.

12. A phonograph pick-up comprising a strai responsive resistance wire mounted betwee spaced apart supports, and a phonograph styli connected to the midpoint of said wire for vary ing the strain in the two halves of said wire 1' accordance with a phonograph record.

13. An apparatus for reproducing phonograp records comprising a, tone arm having space apart supports, a strain responsive resistanc wire connected between spaced apart supports said tone arm, a stylus connected to the midpoix of said wire, a transformer having a center tappe primary Winding, a source of potential connecte between the center tap of said winding and sai phonograph stylus, and means connecting th outer extremities of said transformer winding t the outer extremities of said wire.

14. A phonograph pick-up comprising a strai responsive resistance Wire connected betwee: spaced apart supports, a phonograph stylus con nected to the midpoint of said wire, and mean for balancing the tension in the two halves c said wire.

15. An apparatus for reproducing phonograpl records comprising a tone arm having trans versely arranged spaced apart supports, a straii responsive resistance wire connected betwee] said supports, a phonograph stylus connected it the midpoint of said Wire, a bridge circuit in cluding an inductive impedance connected to th outer extremities of said wire and said phono graph stylus, said circuit including a source 0 direct current connected between said stylus am the midpoint of said impedance.

WILLIAM S. BACHMAN.

REFERENCES CITED The following references are of record in tha 

